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Chapter 7: Performance evaluation of PE system alone in conjunction with background MV and DV systems — airborne infection control 7.1 Introduction and Objective In Chapter 6, the combined PV-PE system was studied under both MV and DV in the context of airborne infection control. One PE was applied for Infected Person while the other PE was combined with PV system for the HP. The observations of combined PV-PE system indicated that using a PE for IP is much more efficient than using PV or combined PV-PE for HP in terms of reducing the exposure to cross-contaminated air. Furthermore, after activating the PE for IP, the use of PV or combined PV-PE for HP may bring more contaminated air to the breathing zone of HP in some configurations. In addition, while Chapter focuses on a normal consultation procedure in healthcare settings with one IP sitting facing the HP, the distance between the HP and the IP is enough for the PV ATD. However, in real situations, Healthy Person (doctor, nurse, etc.) does not always face the Infected Person as a typical position arrangement. More position arrangements with closer distance between the HP and the IP need to be considered. During simple sampling or medical check-ups, the doctor may shift his/her position where the HP no longer faces the IP with a closer distance, or the HP may stand up and come in close proximity to the IP. In these circumstances, HP may move away from his/her consultation desk and there is no space for PV ATD. It is subsequently interesting to know how the PE alone for IP performs when the Healthy Person is exposed to the exhaled contaminated air from IP. It is also important to observe where the protection is strong enough with closer distance, or which configuration would result in higher exposure. In view of these situations, the objective of this chapter explores performance of PE system alone in conjunction with background MV and DV in terms of airborne infection control while Infected Person seated under two different configurations by the side of the seated Healthy Person, as well as when the Healthy Person is standing facing the seated Infected Person. The experimental design and evaluation index are described in Chapter (Section 3.5.4). Experimental chamber is described in Section 3.4.1.1. 7.2 Performance of the PE alone for preventing transmission of exhaled contaminated air in three different positions between IP and HP PE is introduced as a different arrangement in Cases B, C, and D (Figure 7.1). Case B is the shifting of HP to 45 degree to the IP, which can happen during both consultation process and simple medical check-up procedure. Case C is thought to be an example of some careful examination pattern, with both the HP and IP seated. And case D represents the Healthy Person standing close to a seated Infected Person. It is a situation in which the HP has stood up and walked towards the IP to take simple medical test or conduct some simple treatment. In these three cases, the distance between the two manikins is 0.45 m. Figure 7.1 Different arrangements between HP and IP (left: case B, middle: case C, right: case D) 7.2.1 Comparison of iF between the three cases. With a sense of the impact of the background ventilation system on the flow pattern of the indoor air, thus influencing the concentration of exhaled contaminated air at the breathing zone of HP; it is useful to compare the iF of the three cases to determine the effect of background ventilation system and the PE combined background ventilation on HP exposure. Figure 7.2 through Figure 7.5 compare the iF with and without two types of PE with MV and DV. Generally, in all the four Figures, after activating the PE (either top-PE or shoulder-PE) at 10 l/s, iF drops sharply. And the iF is further reduced as the PE flow rate increases from 10 l/s to 20 l/s. MV 1.80E-‐02 1.60E-‐02 1.40E-‐02 iF 1.20E-‐02 Case B 1.00E-‐02 8.00E-‐03 Case C 6.00E-‐03 Case D 4.00E-‐03 2.00E-‐03 0.00E+00 no PE top-‐PE 10l/s top-‐PE 20l/s Figure 7.2 Comparison of iF when using top-PE with MV iF MV 1.80E-‐02 1.60E-‐02 1.40E-‐02 1.20E-‐02 1.00E-‐02 8.00E-‐03 6.00E-‐03 4.00E-‐03 2.00E-‐03 0.00E+00 Case B Case C Case D no PE shoulder-‐PE 10l/s shoulder-‐PE 20l/s Figure 7.3 Comparison of iF when using shoulder-PE with MV DV 1.40E-‐02 1.20E-‐02 iF 1.00E-‐02 8.00E-‐03 Case B 6.00E-‐03 Case C 4.00E-‐03 Case D 2.00E-‐03 0.00E+00 no PE top-‐PE 10l/s top-‐PE 20l/s Figure 7.4 Comparison of iF when using top-PE with DV DV 1.40E-‐02 1.20E-‐02 iF 1.00E-‐02 8.00E-‐03 Case B 6.00E-‐03 Case C 4.00E-‐03 Case D 2.00E-‐03 0.00E+00 no PE shoulder-‐PE 10l/s shoulder-‐PE 20l/s Figure 7.5 Comparison of iF when using shoulder-PE with DV In the baseline cases without any PE switched on with MV; consider the iF of Figure 7.2 and Figure 7.3. It is observed that the iF of case B is the highest, followed by case D, and lastly the case C. This is because with mixing ventilation alone, the airflow with high velocity supplied from the four-way ceiling diffuser generated relatively high turbulence in the occupied zone, thus promoting intensive mixing and spread of exhaled air form IP to the surroundings. Therefore, in case B, the 45 degree between the HP and IP with a short distance of only 0.45 m enables the exhaled air to reach the HP in a higher amount. In Case C, although the IP is exhaling directly towards the HP, the exhaled air does not travel straight to the HP due to the well-mixing effect, thus resulting in the lowest iF. With Displacement Ventilation alone in Figure 7.4 and Figure 7.5, the flow in contact with the Infected Person assisted the free convection flow around the Healthy Person to transport the exhaled contaminated air upward to the breathing zone of HP. Therefore, highest iF is found in case D. In Case C, it could be envisaged that weak mixing and strong stratification in the room is able to promote the lateral dispersion of exhaled air and therefore the exhaled air can travel longer distance to the HP breathing zone. In this case, the IP is also higher compared with case B, in which the IP is exhaling not directly towards the HP. In Figure 7.6, iF is displayed in five groups to compare the values between without PE and with different types of PE. In each of these groups, there are two clusters, each representing the values with MV and DV. 1.80E-‐02 1.60E-‐02 1.40E-‐02 iF 1.20E-‐02 1.00E-‐02 Case B 8.00E-‐03 Case C 6.00E-‐03 Case D 4.00E-‐03 2.00E-‐03 0.00E+00 DV MV DV MV DV MV DV MV DV MV No PE shoulder-‐ top-‐PE 10l/ shoulder-‐ top-‐PE 20l/ PE 10l/s s PE 20l/s s Figure 7.6 Comparison of iF when using different PE configurations The PE combined with total volume ventilation (either MV or DV) always reduces the Intake Fraction in regard to the exhaled air from IP. It is interesting to note that the type of background ventilation system has a substantial impact on the travel of exhaled air. In case B, the MV always leads to a higher iF than DV with or without PE. The infected air is transported to the breathing zone of the HP by the mixing effect around the two persons. The high velocity and turbulence intensity with MV promotes the exhaled air to travel towards the 45 degree direction. Different patterns are observed in case C and case D, where DV results in higher exposure than MV, especially when PE is not used or at a low flow rate of 10 l/s. This is because the DV enhances the forward and upward movement of the exhaled air. By comparing group and group 3, as well as group and group 5, it is seen that for most of the cases, top-PE can lead to a lower iF than shoulder-PE at the same flow rate. This agrees with the observation in Chapter that top-PE has a better performance. 7.2.2 Comparison of Exposure Reduction after using PE The evaluation index Exposure Reduction was described in section 3.5.3. A direct comparison of the PE performance will be made by comparing the exposure reduction for each base case. Figure 7.7 through Figure 7.9 display the Exposure Reduction when applying different PE strategies. The base case using the same flow rate with the same type of PE with MV and DV are not comparable. The top-PE, having a circular cross-section outlet above the head of IP, generated better exposure reduction for most cases. The largest difference is around 40% when the flow rate is 10 l/s with DV in case D. This is because the suction flow together with the upward thermal plume brings more exhaled air to the opening. One exceptional case is when PE is set at 20 l/s with DV in case D, where the exposure reduction while utilizing top-PE is almost the same as using shoulder-PE. With DV in case B, the exposure reduction when using top-PE at 10 l/s is 18% higher than when shoulder-PE is set at 20 l/s; while with MV in case B, the exposure reduction after setting 10 l/s for top-PE is 3% higher than that using 20 l/s of shoulder-PE. Similar to the findings in case B, the results in Figure 7.8 show that a rather lower flow rate of top-PE (10 l/s) reduce more exposure with a higher flow rate of shoulder-PE (20 l/s). The difference is 12% with MV and 10% with DV. The results of this investigation in case D show that the increase of flow rate has a larger impact on the exposure reduction than case B and C. Exposure Reduc2on Case B 100.00% 90.00% 80.00% 70.00% 60.00% 50.00% 40.00% 30.00% 20.00% 10.00% 0.00% Top-‐PE Shoulder-‐PE MV DV MV PE 10l/s DV PE 20l/s Figure 7.7 Comparison of Exposure Reduction in case B Exposure Reduc2on Case C 90.00% 80.00% 70.00% 60.00% 50.00% 40.00% 30.00% 20.00% 10.00% 0.00% Top-‐PE Shoulder-‐PE MV DV PE 10l/s MV DV PE 20l/s Figure 7.8 Comparison of Exposure Reduction in case C Exposure Reduc2on Case D 100.00% 90.00% 80.00% 70.00% 60.00% 50.00% 40.00% 30.00% 20.00% 10.00% 0.00% Top-‐PE Shoulder-‐PE MV DV PE 10l/s MV DV PE 20l/s Figure 7.9 Comparison of Exposure Reduction in case D 7.2.3 Change of Intake Fraction with time For infectious transmission control concerns, both the exposure duration and the concentration of the infection are critical factors. For the three cases with closer distances, higher concentration of exhaled air is measured at the breathing zone of HP, thus the change of iF over the half hour of the three cases when no PE is used is shown in Figure 7.10. In general, the iFs in the three cases increase with time, especially for the first 10 minutes. Consequently, it is supposed to be important to exhaust the exhaled air as early as possible after the IP enters the room. However, in real situation, a Healthy Person would not know if patients are infected or not before the Infected Person is diagnosed and is moved to an isolation room, so the effectiveness of ventilation system in removing the exhaled infectious air in the consulting room becomes important. No PE 0.018 0.016 0.014 Case B +MV iF 0.012 0.01 Case C +MV 0.008 Case D +MV 0.006 Case B +DV 0.004 Case C +DV 0.002 Case D +DV 10 20 30 Time (mins) Figure 7.10 Changes of iF over time when no PE is used Figure 7.11 through Figure 7.16 compare the iF with and without PE over time. It is observed that for all cases, after applying either top-PE or shoulder-PE, the Inhaled Fraction is significantly decreased. With the higher flow rate of 20 l/s of PE, the iFs at 30 minutes are even lower than the ifs at 10 minutes without PE. For example, in Case C with DV, the iF at 10 minutes without PE is as high as 4.85e-3; after the top-PE operates at 20 l/s, the iF is measured at 1.21e-3 at 30 minutes while 2.12e-3 if recorded with the use of shoulder-PE at 30 minutes. This implies that the infection risk is reduced by reducing the exposure amount for longer exposure time. In addition, the iF after activating top-PE is always lower than that when using shoulder-PE at the same flow rate at any time interval. This agrees with the conclusion in Chapter that top-PE performs better than shoulder-PE in terms exhausting the exhaled air. Case B with MV 1.80E-‐02 1.60E-‐02 1.40E-‐02 iF 1.20E-‐02 1.00E-‐02 8.00E-‐03 10mins 6.00E-‐03 20mins 4.00E-‐03 30mins 2.00E-‐03 0.00E+00 Figure 7.11 Changes of iF over time in Case B with MV iF Case B with DV 4.50E-‐03 4.00E-‐03 3.50E-‐03 3.00E-‐03 2.50E-‐03 2.00E-‐03 1.50E-‐03 1.00E-‐03 5.00E-‐04 0.00E+00 10mins 20mins 30mins Figure 7.12 Changes of iF over time in Case B with DV iF Case C with MV 8.00E-‐03 7.00E-‐03 6.00E-‐03 5.00E-‐03 4.00E-‐03 3.00E-‐03 2.00E-‐03 1.00E-‐03 0.00E+00 10mins 20mins 30mins Figure 7.13 Changes of iF over time in Case C with MV iF Case C with DV 9.00E-‐03 8.00E-‐03 7.00E-‐03 6.00E-‐03 5.00E-‐03 4.00E-‐03 3.00E-‐03 2.00E-‐03 1.00E-‐03 0.00E+00 10mins 20mins 30mins Figure 7.14 Changes of iF over time in Case C with DV iF Case D with MV 1.40E-‐02 1.20E-‐02 1.00E-‐02 8.00E-‐03 6.00E-‐03 4.00E-‐03 2.00E-‐03 0.00E+00 10mins 20mins 30mins Figure 7.15 Changes of iF over time in Case D with MV iF Case D with DV 9.00E-‐03 8.00E-‐03 7.00E-‐03 6.00E-‐03 5.00E-‐03 4.00E-‐03 3.00E-‐03 2.00E-‐03 1.00E-‐03 0.00E+00 10mins 20mins 30mins Figure 7.16 Changes of iF over time in Case D with DV 7.3 Air temperature and velocity The room air temperature and mean velocity are recorded at heights of 0.1 m, 0.3 m, 0.7 m, 1.3 m, 1.65 m and 1.95 m using the DANTEC instrument. The vertical room air temperature distribution is presented in Figure 7.17. 23.2 Temperature 23 22.8 22.6 22.4 MV 22.2 DV 22 21.8 0.1m 0.3m 0.7m 1.3m 1.65m 1.95m Height above floor Figure 7.17 Room air temperature with MV and DV The data collected by DANTEC instrument shows the room air temperature at various heights Vertical temperature gradient is observed along the heights of the room with DV, while the temperature profile with MV shows a well-mixed condition. From 0.3 m to 1.3 m, the vertical temperature gradient profiles with DV became steeper, which is the influence of the two seated thermal manikins. The room air mean velocity with MV and DV is presented in Figure 7.18. The higher air movement is observed with MV than DV. The reported velocities were the average values taken at the four locations at each height. 0.25 Velocity 0.2 0.15 MV 0.1 DV 0.05 0.1m 0.3m 0.7m 1.3m 1.65m 1.95m Height above floor Figure 7.18 Room air velocity with MV and DV The results in Figures 7.19 and Figure 7.20 show that the mean air velocity is higher at a height of from 0.3 m to 1.3 m with both MV and DV where the PE was mounted than without PE. This is because the use of the PE enhanced the convection airflow around the thermal manikin, hence increased the air velocities at the locations measured not far from the manikins. It can also be seen that higher the PE flow rate is, higher is the air velocity measured with DV. However, with MV, there is not much difference between PE at 10 l/s and 20 l/s. 0.12 0.1 Velocity 0.08 No PE 0.06 PE 10l/s 0.04 PE 20l/s 0.02 0.1m 0.3m 0.7m 1.3m 1.65m 1.95m Height above floor Figure 7.19 Room air velocity with and without PE with DV MV 0.25 Velocity 0.2 0.15 No PE 0.1 PE 10l/s 0.05 PE 20l/s 0.1m 0.3m 0.7m 1.3m 1.65m 1.95m Height above floor Figure 7.20 Room air velocity with and without PE with MV The results in Figures 7.21 and 7.22 show that the Infected Manikin was prone to higher air velocities at neck/ear region where the PE were switched on than without PE. The velocity increases as the PE flow rate increases. When the results obtained with shoulder-PE are compared with the results obtained with the top-PE, it is observed that shoulder-PE generated higher velocity at neck/ear region of the Infected Manikin, especially with DV. This implies that the shoulder-PE which is located near to the neck/ear region may lead to higher air movement around the head. MV 0.3 Air Velocity 0.25 0.2 0.15 0.1 0.05 No PE PE 10l/s PE 20l/s shoulder-‐PE 0.17 0.235 0.28 top-‐PE 0.17 0.23 0.25 Figure 7.21 Local air velocity at neck/ear region with MV Air velocity DV 0.35 0.3 0.25 0.2 0.15 0.1 0.05 No PE PE 10l/s PE 20l/s shoulder-‐PE 0.11 0.25 0.29 top-‐PE 0.11 0.15 0.18 Figure 7.22 Local air velocity at neck/ear region with DV Figure 7.23 and Figure 7.24 show the Draft Rating (DR) in the space close to the manikin’s neck/ear region (1.2 m). Higher draft rating is recorded after switching on the PE. Since the draft is an unwanted local cooling of the body caused by air movement, the increase of draft rating is not preferred. The figures show that the increase of PE flow rate also brings an increase of DR at the neck/ear. With the higher flow rate of PE (20 l/s), the DR increases to more than 15%, and a value of around 15% is observed with the lower flow rate of 10 l/s. This means that further consideration is needed when using PE regarding the draft risk. MV 25.00% DraH Ra2ng 20.00% 15.00% shoulder-‐PE 10.00% top-‐PE 5.00% 0.00% No PE PE 10l/s PE 20l/s Figure 7.23 Draft rating at neck/ear region of IP with MV DraH Ra2ng DV 18.00% 16.00% 14.00% 12.00% 10.00% 8.00% 6.00% 4.00% 2.00% 0.00% shoulder-‐PE top-‐PE No PE PE 10l/s PE 20l/s Figure 7.24 Draft rating at neck/ear region of IP with DV 7.4 Key Findings The major findings from this particular study on the influence of different arrangement between HP and IP, PE types and PE flow rate, and back ground ventilation type to the airborne transmission contaminated air exhaled by an IP are as follows: The type of background air distribution system has an impact on the flow pattern of exhaled air. With MV, when PE is not used, the highest exposure possibility is when the HP and IP are 45 degrees to each other (case B). Case C (HP and IP are 90 degree to each other) will lead to the lowest exposure of exhaled contaminated air. With DV, case D (HP standing facing the seated IP) will result in highest exposure of the HP while case B can achieve the best protection for the HP among the three cases when PE is not switched on. After using either shoulder-PE or top-PE, the transmission of exhaled air to the HP’s breathing zone is largely reduced. The performance of top-PE is better than that of the shoulder-PE since it achieves better protection with lower flow rate, thus saving energy and reducing the noise level. For infectious transmission control concerns, both the exposure duration and the concentration of the infection are critical factors. The longer the IP stays in the consulting room, the higher the exposure and risk for the HP. By using PE for the IP, the exposure at 30 minutes after entering the consultation room of the IP is lower than the exposure at 10 minutes without PE. However, there is a draft risk (Draft Rating is more than 15%) potential after using the PE. Further investigation on the subjective acceptability of PE may be needed. [...]... Figure 7. 24 Draft rating at neck/ear region of IP with DV 7. 4 Key Findings The major findings from this particular study on the influence of different arrangement between HP and IP, PE types and PE flow rate, and back ground ventilation type to the airborne transmission contaminated air exhaled by an IP are as follows: The type of background air distribution system has an impact on the flow pattern of. .. (1.2 m) Higher draft rating is recorded after switching on the PE Since the draft is an unwanted local cooling of the body caused by air movement, the increase of draft rating is not preferred The figures show that the increase of PE flow rate also brings an increase of DR at the neck/ear With the higher flow rate of PE (20 l/s), the DR increases to more than 15%, and a value of around 15% is observed... 2.00E-‐03 0.00E+00 10mins 20mins 30mins Figure 7. 15 Changes of iF over time in Case D with MV iF Case D with DV 9.00E-‐03 8.00E-‐03 7. 00E-‐03 6.00E-‐03 5.00E-‐03 4.00E-‐03 3.00E-‐03 2.00E-‐03 1.00E-‐03 0.00E+00 10mins 20mins 30mins Figure 7. 16 Changes of iF over time in Case D with DV 7. 3 Air temperature and velocity The room air temperature and mean... 7. 00E-‐03 6.00E-‐03 5.00E-‐03 4.00E-‐03 3.00E-‐03 2.00E-‐03 1.00E-‐03 0.00E+00 10mins 20mins 30mins Figure 7. 13 Changes of iF over time in Case C with MV iF Case C with DV 9.00E-‐03 8.00E-‐03 7. 00E-‐03 6.00E-‐03 5.00E-‐03 4.00E-‐03 3.00E-‐03 2.00E-‐03 1.00E-‐03 0.00E+00 10mins 20mins 30mins Figure 7. 14 Changes of iF over time in. .. heights of 0.1 m, 0.3 m, 0 .7 m, 1.3 m, 1.65 m and 1.95 m using the DANTEC instrument The vertical room air temperature distribution is presented in Figure 7. 17 23.2 Temperature 23 22.8 22.6 22.4 MV 22.2 DV 22 21.8 0.1m 0.3m 0.7m 1.3m 1.65m 1.95m Height above floor Figure 7. 17 Room air temperature with MV and DV The data collected by DANTEC instrument shows the room air. .. 0.3m 0.7m 1.3m 1.65m 1.95m Height above floor Figure 7. 18 Room air velocity with MV and DV The results in Figures 7. 19 and Figure 7. 20 show that the mean air velocity is higher at a height of from 0.3 m to 1.3 m with both MV and DV where the PE was mounted than without PE This is because the use of the PE enhanced the convection airflow around the thermal manikin, hence increased the air velocities... After using either shoulder-PE or top-PE, the transmission of exhaled air to the HP’s breathing zone is largely reduced The performance of top-PE is better than that of the shoulder-PE since it achieves better protection with lower flow rate, thus saving energy and reducing the noise level For infectious transmission control concerns, both the exposure duration and the concentration of the infection... 20l/s 0 0.1m 0.3m 0.7m 1.3m 1.65m 1.95m Height above floor Figure 7. 20 Room air velocity with and without PE with MV The results in Figures 7. 21 and 7. 22 show that the Infected Manikin was prone to higher air velocities at neck/ear region where the PE were switched on than without PE The velocity increases as the PE flow rate increases When the results obtained with shoulder-PE are... 0. 17 0.23 0.25 Figure 7. 21 Local air velocity at neck/ear region with MV Air velocity DV 0.35 0.3 0.25 0.2 0.15 0.1 0.05 0 No PE PE 10l/s PE 20l/s shoulder-‐PE 0.11 0.25 0.29 top-‐PE 0.11 0.15 0.18 Figure 7. 22 Local air velocity at neck/ear region with DV Figure 7. 23 and Figure 7. 24 show the Draft Rating (DR) in the space close to the manikin’s... longer the IP stays in the consulting room, the higher the exposure and risk for the HP By using PE for the IP, the exposure at 30 minutes after entering the consultation room of the IP is lower than the exposure at 10 minutes without PE However, there is a draft risk (Draft Rating is more than 15%) potential after using the PE Further investigation on the subjective acceptability of PE may be needed . Chapter 7: Performance evaluation of PE system alone in conjunction with background MV and DV systems — airborne infection control ! 7. 1 Introduction and Objective In Chapter 6, the combined. observations of combined PV-PE system indicated that using a PE for IP is much more efficient than using PV or combined PV-PE for HP in terms of reducing the exposure to cross-contaminated air. Furthermore,. Comparison of iF between the three cases. With a sense of the impact of the background ventilation system on the flow pattern of the indoor air, thus influencing the concentration of exhaled contaminated